shapely.MultiPolygon does not support overlapping geometry

[hohlraum]

This is an issue since MultiPolygon is used to represent Elements as shapely objects.

>>>d1 = shapes.Disk((10,0), 15)
>>>d2 = shapes.Disk((-10,0), 15)
>>>d1.shape.is_valid
True
>>>e = core.Elements([d1,d2])
>>>e.shape.is_valid
False

Further boolean operations on e will fail.

[tom-varga]

Could shapely's cascaded_union operator be used to merge overlapping polygons in a MultiPolygon?
I think a polygon merge capability should be added to the list of boolean operators in any case.